The invention relates to a locking device for a lock, especially for a ring lock, comprising a connecting part and a connecting part case with a snap-in locking device operated with a locking mechanism, which allows in a basic position of the locking mechanism insertion of the connecting part, but prevents withdrawal of the connecting part and which allows in an open state of the locking mechanism withdrawal of the connecting part, a ratchet shoulder fitted to the connecting part and the snap-in locking device having at least one ratchet body being transversely movable and lockable with respect to the inserting direction of the connecting part to engage behind the ratchet shoulder.